Wheel suspensions of vehicles are normally provided with spring action devices and damping devices in order to improve comfort and driving ability of the vehicle. A MacPherson spring leg is a common type of such a device, in which a compressible screw spring surrounds a hollow tube leg containing a hydraulic damping cylinder. Alternatively the screw spring may be separately arranged relative to the damping cylinder.
Also combined, so called hydro-pneumatic spring and damping devices have been suggested. For example the not pre-published Swedish patent application 0702481-3 describes different embodiments of hydro-pneumatic spring and damping devices, which are devised in such a way that inward spring action and outward spring action of the wheel suspensions may be controlled in a desired manner in order to e.g. improve driving ability of the vehicle, as the vehicle is subjected to heeling and kneeling movements during drive on road and in terrain.
In known wheel suspensions with spring action devices or damping devices of the above mentioned type the damping cylinder is normally mounted in such a way that the piston is pressed into the cylinder during inward spring action of the wheel undercarriage and is expressed out of the cylinder during outward spring action. This results in increased buckling and bending strain of the piston and increased ware and shorter life expectancy on sealings belonging thereto.
A wheel suspension is known from JP 8-156548, in which a damping cylinder indeed is mounted in such a way between an upper supporting arm and a lower fixed frame part that the piston is expressed from the cylinder during inward spring action of the wheel undercarriage and is pressed into the cylinder during outward spring action. This wheel suspension needs to be supplemented by a separate mechanical spring device and has, due to the attachment of the cylinder in the upper supporting arm, a higher unsprung mass, which requires more energy in order to damp the unsprung mass, whereby the damper becomes warmer due to kinetic energy from the wheel being converted to heat by the restrictions in the damper. Also, its linked arm system does not facilitate high belly clearance of the vehicle or minimizes the track gauge changes during inward and outward spring actions or results in comfort properties which a hydro-pneumatic spring leg may provide.